Many types of gas flow controllers have been implemented for a variety of applications. For example, many known control arrangements for gas burners include a main valve, a servo valve and a servo controller, wherein the servo controller serves to control a gas output pressure by controlling the opening of the main valve.
For modulating the gas outlet pressure, an actuator is provided for the servo valve and achieves an opening and closing of the servo valve at the pertinent frequency, which can be modulated.
FIG. 2 shows one such gas flow controller to which various implementations of the present invention may be applicable. This controller comprises a main valve, the valve head 21 of which cooperates with a valve seat 22 and is loaded by a spring 30 into its closing position. The valve head 21 is connected to a diaphragm 23 above which a first gas chamber 24 is provided. The gas flows from the inlet 34 into the second gas chamber 25 and can flow on into the third gas chamber 31 when the main valve is open, and from there to the outlet 35. If the main valve is closed, a gas flow is prohibited. In the closing position, the two-way valve 29, which is operable electrically, is in its closed position. The two-way valve 29 is held in this position due to an appropriate pressure difference in the gas chambers 24, 25 acting on the diaphragm, and due to the force of the spring 30 acting on the valve seat 21. Thus, gas flows into the first gas pipe 27 through the second gas pipe 26 which has a certain resistance adapted, if necessary, to be influenced by a throttle 32, since a flow through the two-way valve 29 is not possible due to the closed position of the same.
If there is a pressure equalization between the first gas chamber 24 and the second gas chamber 25, the main valve is nevertheless securely held in its closed position, since it is loaded into the closed position by the pressure spring 30. If the two-way valve 29 is opened, gas flows via the first gas pipe 27 and the second gas pipe 26 through the two-way valve 29 into the third gas pipe 28 ending in the third gas chamber 31. The pipe portion upstream of the two-way valve 29 and through the two-way valve 29 shows a certain flow resistance that can, if necessary, be influenced by a throttle 33. Thus, gas flows out of the first gas chamber 24 until the gas pressures in the first gas chamber 24 and in the third gas chamber 31 are equal. Furthermore, no additional gas flows via the first and second gas pipes 27, 26 into the first gas chamber 24, as this rather flows via the two-way valve 29 into the third gas pipe and, thus, into the third gas chamber 31.
Accordingly, if the two-way valve 29 is shut again, i.e., if a flowing-off via the third gas pipe 28 into the third gas chamber 31 is impossible, there is another pressure equalization between the first gas chamber 24 and the second gas chamber 25, with the result that the main valve closes again. It is obvious that, for the mode of operation of this control means, the coordination of the pipe resistances is of major importance. Such control means must have a certain minimum closing speed. Thus, to allow an appropriately quick closing of the main valve, the pipe resistances have to be coordinated accordingly. Furthermore, a certain opening speed has to be ensured and, of course, a certain maximum opening of the main valve, ensuring the desired gas flow from the inlet 34 to the outlet 35. No pressure modulation by mere adjustment of a certain differential pressure between the first gas chamber 24 and the second gas chamber 25 is possible with this controller. The cross-sections and flow resistances of the gas pipes are coordinated such that the required and desired opening and closing speeds are reached. Thus, when the two-way valve 29 is opened, the main valve is automatically taken into its open position at a predetermined speed, whereas, when the two-way valve 29 is closed, a complete closing of the main valve sets in along with the desired closing speed. Thus, a pressure modulation is only possible if the servo two-way valve 29 is operated in a pulsed manner with the pulse width being modulatable.